A typical photographic element contains multiple layers of light-sensitive photographic silver halide emulsions with one or more of these layers being spectrally sensitized to each of blue light, green light and red light. The blue, green and red light-sensitive layers typically contain yellow, magenta, and cyan dye-forming couplers, respectively.
For forming color photographic images, the color photographic material is exposed imagewise and processed in a color developer bath containing an aromatic primary amine color developing agent. Image dyes are formed by the coupling reaction of these couplers with the oxidized product of the color developing agent.
Generally, image couplers are selected according to their ability to couple efficiently with oxidized color developer, thus minimizing the necessary amounts of coupler and silver halide emulsion in the photographic element; to provide image dyes whose hues are appropriate for the particular photographic application in which they are used; to provide image dyes whose absorption spectra have low unwanted side absorptions and thus lead to good color reproduction; to provide image dyes with good stability to heat, light, and ferrous ions which are present in the bleaching solution; and to provide good physical and chemical properties such as good solubility in coupler solvents, and good dispersibility in gelatin.
In recent years, a great deal of study has been conducted to improve dye-forming couplers for silver halide photosensitive materials in terms of improved color reproducibility and image dye stability. However, further improvements are needed, particularly in the area of cyan couplers.
The couplers used to form cyan image dyes are generally derived from naphthols and phenols, as described, for example, in U.S. Pat. Nos. 2,367,351, 2,423,730, 2,474,293, 2,772,161, 2,772,162, 2,895,826, 2,920,961, 3,002,836, 3,466,622, 3,476,563, 3,552,962, 3,758,308, 3,779,763, 3,839,044, 3,880,661, 3,998,642, 4,333,999, 4,990,436, 4,960,685, and 5,476,757; in French patents 1,478,188 and 1,479,043; and in British patent 2,070,000. These types of couplers can be used either by being incorporated in the photographic silver halide emulsion layers or externally in the processing baths. In the former case the couplers must have ballast substituents built into the molecule to prevent the couplers from migrating from one layer into another. Although these couplers have been used extensively in color photographic film and paper products, the dyes derived from them still suffer from poor stability to heat, humidity or light, low coupling efficiency or optical density, and in particular from undesirable blue and green absorptions which cause considerable reduction in color reproduction and color saturation.
The hue of a dye is a function of both the shape and the position of its spectral absorption band. Traditionally, the cyan dyes used in color photographic papers have had nearly symmetrical absorption bands centered in the region of 620 to 680 nm, preferably 630 to 660 nm, and more preferably 635 to 655 nm. Such dyes have rather large amounts of unwanted absorption in the green and blue regions of the spectrum.
More desirable would be a dye whose absorption band is asymmetrical in nature and biased towards the green region, that is, with a steep slope on the short wavelength side. Such a dye would suitably peak at a shorter wavelength than a dye with symmetrical absorption band, but the exact position of the desired peak depends on several factors including the degree of asymmetry and the shapes and positions of the absorption bands of the magenta and yellow dyes with which it is associated.
Cyan couplers which have been recently proposed to overcome some of these problems are 2,5-diacylaminophenols containing a sulfone, sulfonamido or sulfate moiety in the ballasts at the 5-position, as disclosed in U.S. Pat. Nos. 4,609,619, 4,775,616, 4,849,328, 5,008,180, 5,045,442, and 5,183,729; and Japanese patent applications JP02035450 A2, JP01253742 A2, JP04163448 A2, JP04212152 A2, and JP052041 10 A2. Even though cyan image dyes formed from these couplers show improved stability to heat and humidity, enhanced optical density and resistance to reduction by ferrous ions in the bleach bath, the dye absorption maxima (.lambda.max) are too bathochromically shifted (that is, shifted to the red end of the visible spectrum) and the absorption spectra are too broad with considerable amounts of undesirable blue and green absorptions. Thus, these couplers are not practical for use in color papers.
Although the use of sulfone (--SO.sub.2 --) groups in the ballast moieties of phenolic cyan couplers has been described in various publications cited above, the coupler structures disclosed therein do not possess the combination of essential moieties in the ballasts that can provide the desired reduction in unwanted green and blue absorption, which would result in improved color reproduction and color saturation in color photographic papers.
Accordingly, there has been a need to provide a photographic element containing cyan dye-forming couplers which do not have the inherent disadvantages of the known couplers. It is therefore an object of this invention to provide a cyan dye-forming coupler which exhibits excellent photographic properties such as coupling efficiency, and whose dye has excellent stability to heat and light and exhibits improved color reproduction and saturation.